Beta-Oxidation of fatty acids is a principal energy yielding pathway in liver and heart. A knowledge of metabolic regulation of Beta-oxidation is essential to understand the control of fatty acid metabolism especially in diseases such as diabetes that perturb fatty acid oxidation. We propose to study the three-dimensional structure of the general fatty acyl Coa dehydrogenase, that catalyzes the dehydrogenation of acyl CoA thiolesters. This enzyme has recently been under intensive investigation and some progress has been made in elucidating the catalytic and structural properties of the enzymes; however, attempts to relate the chemical functions to the structure of the protein have been limited by lack of detailed structural information. The availability of the porcine liver general acyl-CoA dehydrogenase in a crystal form suitable for x-ray analysis permits the three dimensional structure of this representative enzyme to be determined. This enzyme has a molecular weight of 180,000 and contains four identical subunits, each containing one equivalent of flavin adenine dinucleotide. The crystals have one monomer per asymmetric unit. It is proposed first to carry out a low resolution analysis (6.0 Angstroms) to determine the general shape of the enzyme, the location of the flavin and the binding site for substrate. Subsequently it is proposed to initiate a high resolution analysis for use in elucidating and detailed mechanism of action in the oxidation of acyl-Coa thioesters and in transfer of electrons to the electron transfer flavoprotein, the physiological oxidant of the dehydrogenase in the mitochondrion.